To be honest.. i really think there wasn't a dark age.
The notion of all science and invention suddenly stopping after the fall of the roman empire is in my mind victorian psudeo-history judgementalism at it's worse. For example, 'rome' never really fell at all. It continued in the east until the 1450's.
However, i'll admit literacy and writing did drop off steeply. But there still existed proper academia. Take the Venerable Bede (born AD 672), the sage of Sunderland. His history of the English people, written in excellent clear Latin of the day, is one of the great works of English history.
The term 'dark age' itself is far less common than it used to be. It has fell out of disuse mainly because of the negative connotations. If anything, the dark age it self is more of a collection of lulls in each country that span more or less 500 years across europe. It's therefore wrong to claim there's one dark age if there even was one and instead to refer to a collection of 'dark ages'
Further reading: http://www.academia.edu/3313369/There_was_nothing_dark_about_the_Dark_Ages_The_Medieval_Origins_of_Science
Religious authority
impeding recovery of Roman sources
NO.
I understand that I'm being blunt there, but NO. Monasteries are famous for preserving and copying classical works. This situation came about for two main reasons. Firstly, many monasteries had relatively large libraries and were populated by learned, well-off people. Not just anyone could become a Benedictine monk, and having to pay your way in either directly in cash or indirectly through material donations was quite common.
Secondly, monasteries were intended as places of hard work, as labour was felt to be a way of getting closer to God - and I don't know if you've tried it recently, but copying out an entire book by hand is hard, even without decorating it. While gardening and other chores that more immediately spring to mind when we say "hard work" were an important part of monastic life, copying classical texts was majorly important to your average monk as well.
Also, "dark ages" is just wrong.
If you would like to know more, Yale put up one of their Open Yale courses on the Early Middle Ages:http://oyc.yale.edu/history/hist-210#sessions
Lectures 12 and 13 should be especially interesting to you, but the whole thing is just fabulous.
There are many, many questions about the 'Dark Ages' in the FAQ. You could start here, or with one of these questions:
The whole concept of a Dark Age is a later (and outdated) categorization of the centuries following the breakdown of effective Roman authority in Western Europe. It is an arbitrary designation. At times it has referred to the entire 1000 year period traditionally ascribed to the Middle Ages, at others only the first few centuries, and sometimes only a few places, at different times, and intermittently. 'Dark' has the connotation of backwardness, grimness, ignorance, and doom- these are all comparative judgments that spring from the label-makers assumed values of what is good and what is bad. Things certainly changed in the West; there was a decline in international trade (though not for prestige goods) and a general breakdown of pan-Mediterranean authority (though the Eastern Romans give that claim a run for its money at certain points), as well as general decrease in urban population centers and overall learning/literacy. These are changes- nothing more. I know it may seem unhelpful, but historians try to cultivate and attitude of understanding vs. judgment in their approach to past events, i.e. 'why/how did x event/change occur' and 'x event was bad'. From an academic standpoint, the conscious use of the word 'dark' immediately introduces bias into our reading of the past. In other words, to label the past as 'Dark' colors our approach to our studies, it keeps us from being objective, meaning we might miss or ignore things like the Carolingian Renaissance, the innovation of Irish monasticism, the complexity and nuance of medieval theology, and the achievements of the Byzantines, because, 'No, it was a dark age- Europe was dark.'
Ultimately, the understanding of history solely in terms of progress is teleological and misses out on important knowledge that underlies eras of social, political, economic, cultural, etc., etc. change
As far as religion goes- the theory that Christianity caused the collapse and stunted the 'progress' of human knowledge is not one that has been seriously considered since the 19th century; but for some reason the Conflict Thesis (that religion and science are diametrically opposed) continues to be popular among certain segments of the general public. No contemporary academic that I am aware of seriously considers this view. The Church and monastic communities across Europe preserved learning and understanding that had been lost elsewhere in the West. People sometimes forget that the Middle Ages constituted 1000 years of history (the time between 1000 CE and now) and the people who lived and worked, studied and learned, were innovative and forward thinking in their own right. Things were lost, but it's not as if people sat on their bums and twiddled their thumbs for a millennium, waiting for someone to hand them a copy of Plato's Republic.