The Church began after the ascension of Jesus. Before this time there were Synagogues. Jesus Christ"s life and death was foretold and predicted in the old Testament, and according to Scripture, Christ is the Head of the Church. Likewise, according to scripture, Jesus Christ is the same yesterday, today, and forever. This tells me that the Scripture, which is the Word of God given to the various writers by the Holy Spirit, is the only Authority for the Church.
The authority of church lies only on the church and its beliefs. Some churches may decide to follow and listen to scripture without any outside beliefs, while other churches may choose a different path. In the end, it just depends on the people involved and those who are actually running the church.
The authority of the Church lies first and foremost within every human heart. The Church is nothing in itself; the Church consists of people and people's souls. If we relied on the authority of scripture, we would be poking peoples' eyes out and stoning people. We would be starting wars and killing our siblings. Are these things holy? I think not.
The authority of the church may rely on scripture from time to time, but I would not say that that is only where that church may get their authority. Many different churches like to run things slightly differently, or try to be as unique as possible, so I would say that authority comes from the church members.